The interaction of the cancer chemotherapeutic agent cis-diamminedichloroplatinum(II) (cis-DDP) with DNA appears essential to the action of the drug. The efficacy of the drug can be modulated by the capacity of a cell to repair the damaged DNA or to efficiently replicate on damaged templates. However, these systems are not infallible and toxicity and mutagenicity do result. I intend to investigate these phenomena in murine leukemia L1210 cells and in a cis-DDP resistant subline. DNA of both cell lines can be equally platinated, therefore, resistance appears to reflect a differential capacity of the cells to deal with the damage. Initial experiments will characterize the interaction of cis-DDP with DNA and then be extended to the formation and removal of cis-DDP lesions in L1210 cells. The enzymology of this repair process will be analyzed. Several approaches will be used to investigate the effect of lesions on DNA synthesis. These include an analysis of the size of newly synthesized DNA, its ligation and possible recombination. DNA of known base sequence will be used to determine sites of inhibition of replication. Mutagenesis in a whole cell system will be investigated specifically in the adenine phosphoribosyl transferase gene, an easily selectable mutant. It is proposed that resistance to cis-DDP may be mediated by a gene amplification process and an attempt will be made to isolate the gene and then the gene product(s) involved. The involvement of aberrant replication in the development of resistance will be assessed.